The present invention relates to energy absorbing bumpers specifically, a light weight bumper presenting a soft collision interface to objects on impact, and having a relatively wide, effective angle of collision acceptance. Although various fluids may be employed in such bumpers, the utilization of air as the working fluid not only produces a lighter weight assembly, but also obviates the need for seasonal maintenance which is necessary in some climates where liquids are employed.
Recent Department of Transportation (DOT) requirements have stimulated development of a suitable energy absorbing bumper system for motor vehicles. Although pneumatic energy absorbing bumper designs have been known since 1898, when they were first utilized with railway carriages, many of the present design proposals do not differ appreciably from the early configurations.
Generally, pneumatic bumpers absorb energy as they are compressed. Bumpers which are entirely closed offer increased resistance to compression, as they are subjected to increased forces of impact or peak loads, inasmuch as the latent air therein must actually expand the flexible structure. For this reason, static pressure within the bumper cannot be too high or the structure may rupture on impact. Alternatively, if the structure does not rupture, its lack of compression may permit damage to occur since the forces of impact will be transferred to both the impacted and the impacting object. Insofar as such bumpers contain no energy dissipating valving, whereby the compressed air may be released, they function primarily as energy storing devices rather than energy dissipating systems and as such tend to act as a spring, imparting a potentially harmful rebound effect immediately subsequent to impact with another object.
One relatively recent design involving a type of closed system pneumatic bumper is embodied in U.S. Pat. No. 3,810,668 and includes an inflatable bumpoer portion which is vented directly to a storage tank through suitable conduits. Prior to impact, pressures within the bumper and the tank are at equilibrium and immediately following impact, most of the working fluid is driven from the bumper to the tank with an increase in pressure therein. The fluid subsequently bleeds back into the bumper until equilibrium again obtains.
A pneumatic bumper which vents its air to another closed system such as a tank may be considered an improvement over the totally closed structure in some respects; however, certain problems with the former system are merely lessened and not eliminated. For example, upon compression of the flexible bumper, air is driven therefrom, but as more of that air is transferred to the tank and the pressure increases therein, the bumper itself resists further compression thereby limiting its capacity to absorb energy. Nor, can relatively higher static pressures be maintained in the bumper to tank system, inasmuch as both pressures must be at equilibrium prior to impact. If the air pressure within the bumper and tank are both relatively high in this context, e.g., greater than 10 psig, transfer of the air from the bumper to the tank becomes more difficult. Furthermore, the tank itself must be strong enough to resist rupturing, adding even more weight to the vehicle. Increased bumper weight, particularly when it is in the front bumper which necessarily is located forward of the front axle of a vehicle, contributes to problems such as increased tire wear and sluggish steering response.
Another relatively recent design involving a pneumatic bumper is embodied in U.S. Pat. No. 3,768,850 and includes a resiliently deformable bumper shell mounted on a supporting plate. A plurality of ribs extend from the inner walls of the bumper shell to the supporting plate where they are removably connected in grooves. Mounting of the ribs in the grooves and the bumper shell itself to the supporting plate produces a plurality of individual chambers, normally closed to the atmosphere. At the rear of each chamber is a pressure relief valve which vents increasing chamber pressures, encountered during impact, directly to the atmosphere. Subsequent to impact, the bumper slowly returns to its original shape by restricted flow of air through the valves and into the chambers.
Despite the ability of such a bumper to dissipate energy, i.e., by exhausting the air under pressure to the atmosphere, peak loading forces which compress the bumper are undesirably high due to its internal structure. That is, the configuration of the ribs, effectively connecting the front impacting face of the bumper shell to the rear supporting plate, inhibits the rate at which the bumper shell will collapse as well as increases the forces necessary to cause total collapse of the bumper. Insofar as energy absorption and dissipation are functionally dependent upon the compression, or rapid decrease of internal bumper volume, it is believed that absorption of energy in such a system will be performed primarily by the resilient bumper with a relatively small amount of the energy being absorbed by the air contained therein. Based upon experimental work and development of the present bumper system, as well as the system set forth in our parent application, Ser. No. 426,615, it has been found that greater amounts of energy may be dissipated by proper use of the air contained therein rather than relying solely on the elastomer itself.
Thus, it is believed that a bumper such as embodied in U.S. Pat. No. 3,638,985, which may be characterized as nonpneumatic in the sense that the interior of the bumper is always in direct communication with the atmosphere, would be incapable of dissipating a satisfactory amount of the energy that it absorbs upon impact inasmuch as neither air nor other working fluid could be utilized to any appreciable degree in such capacity. Total energy absorption and whatever dissipation may be obtained would be solely dependent upon the elastomeric nature of the material forming the bumper.
As pneumatic bumpers of either of the foregoing types inherently absorb energy during compression, the problem has been that to obtain a maximum degree of compression, the impacting or peak loading force which compresses the bumper is often so high that harmful forces are transferred during collision rather than absorbed because the bumper cannot be readily compressed.